A molecular sieve is generally a microporous structure composed of either crystalline aluminosilicate, belonging to a class of materials known as zeolites, or crystalline aluminophosphates, or crystalline silicoaluminophosphates. Molecular sieves can be made by hydrothermal crystallization from a reaction mixture comprising reactive sources of silicon and/or aluminum and/or phosphorous containing compounds, usually in the presence of one or several organic amines or quaternary ammonium salts as structure directing agents, also known as templates.
Molecular sieve catalysts are compositions made of molecular sieve particles bound together to form particles larger than the molecular sieve components. The molecular sieve catalyst particles can also include other components such as binders, fillers, like clay, and optionally other catalytically active agents such as rare earth metal oxides, transition metal oxides, or noble metal components.
Conventional methods of making molecular sieve catalyst particles include mixing together molecular sieve and binder, as well as other optional components such as fillers and other catalytic components. The mixture is typically stirred in solution to form a slurry, and the slurry is dried to form molecular sieve catalyst particles. Following drying, the particles are calcined to harden, as well as activate, the catalyst particles.
For example, U.S. Pat. No. 6,509,290 B1 (Vaughn et al.) discloses a method of making molecular sieve catalyst, the catalyst containing molecular sieve attrition particles and virgin molecular sieve. The attrition particles are essentially broken particles that have been recycled from a catalyst manufacture process or a reaction system. The method involves mixing together a molecular sieve, virgin binders and fillers, spray dried attrition particles or clumps, and non-virgin attrition particles from a reaction unit. The mixture is dried to form finished catalyst particles. To add strength to the finished catalyst particles, the attrition particles are substantially free of coke.
U.S. Pat. No. 6,153,552 (Wachter et al.) describes another method for making molecular sieve catalyst. The method involves mixing together a molecular sieve and an alumina sol, the alumina sol being made in solution and maintained at a pH of 2 to 10. The mixture is then spray dried and calcined. The calcined product is reported to be relatively hard, i.e., attrition resistant.
Certain catalytic reaction processes, particularly processes which convert oxygenates to olefins, require very hard molecular sieve catalyst compositions to survive the rigorous commercial scale reaction conditions over a relatively long period of time. Conventional methods of making molecular sieve catalysts fail to consistently achieve an appropriate hardness for effective commercial scale use. Additional methods are, therefore, needed for the manufacture of molecular sieve catalyst particles that are sufficiently hard to withstand rigorous commercial scale reaction conditions.